The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
One goal of a network manager is to control total cost of ownership of the network. Cabling problems can cause a significant amount of network downtime and can require troubleshooting resources, which increase the total cost of ownership. Providing tools that efficiently solve cabling problems may increase network uptime and reduce the total cost of ownership.
Referring now to FIG. 1, conventional cable testers 10 are frequently used to isolate cabling problems. The cable testers 10 are coupled by a connector 12 (such as an RJ-45 or other connector) to a cable 14. A connector 15 connects the cable to a load 16. The cable testers 10 typically require the load 16 to be a loop back module. The cable testers 10 perform cable analysis and detect a short, an open, a crossed pair, or a reversed pair in the cable 14. A short or an open may be detected without a load. The cable testers 10 can also determine a length of the cable 14 and a distance from one end of the cable 14 to a point where the cable 14 has a fault such as a short or an open condition.
For example, in a multi-conductor cable, a short condition occurs when two or more conductors in the cable 14 are short-circuited together. An open condition occurs when one or more conductors in the cable 14 lack continuity between both ends of the cable 14. A crossed pair occurs when a pair of conductors communicates with different pins at each end of the cable 14. For example, a first pair may communicate with pins 1 and 2 at one end and pins 3 and 6 at the other end. A reversed pair occurs when two ends in a pair are connected to opposite pins at each end of the cable 14. For example, a conductor connected to pin 1 on one end communicates with pin 2 at the other end, and a conductor connected to pin 2 on one end communicates with pin 1 at the other end.
The cable testers 10 employ time domain reflectometry (TDR), which is based on transmission line theory, to troubleshoot cable faults. The cable testers 10 transmit a pulse 17 on the cable 14 and analyze a reflection or a return pulse 18 when received. Specifically, the cable testers 10 measure a difference between a time when the pulse 17 is transmitted and a time when the return pulse 18 is received. Additionally, the cable testers 10 analyze characteristics such as shape and size of the return pulse 18 relative to the pulse 17 that is transmitted. By comparing the pulses 17 and 18 and based on electrical properties of the cable 14 such as a cable propagation constant, a cable distance can be estimated and a fault can be identified.
Conventional cable tests, however, may generate inaccurate results when the cable 14 is terminated by an active link partner generating link signals during a test. For example, TDR cannot determine cable length when the link is active, that is, when the link partner at the remote end of the cable 14 is active or in use. This is because the remote end of the cable 14 is properly terminated when the link partner is active. When the remote end of the cable 14 is properly terminated, the cable 14 functions as a substantially balanced transmission line. That is, when the remote end receives a TDR pulse, the remote end may return a very weak signal. Weak return signals cannot be analyzed unless extensive electronic circuits are used. Implementing extensive electronic circuits, however, can be expensive and may not be feasible in low-cost systems.
On the other hand, digital signal processing (DSP) can determine cable length when the link is active. In DSP, unlike in TDR, no pulses are injected into the cable 14. Instead, parameters such as amplitude, pulse width, pulse shape, etc., of signals that are normally transmitted and received on the cable 14 are measured to determine cable length. DSP, however, involves making some assumptions and therefore yields cable length measurements that are approximate rather than accurate.
For example, if cable length is determined based on amplitude of a received signal, the amplitude of the transmitted signal is generally unknown or unknowable and therefore needs to be assumed. Additionally, any attenuation in the received signal is calculated by assuming an average attenuation per unit length of the cable 14. Therefore, the length of the cable 14 determined using DSP is generally an approximate estimate rather than an accurate measurement.
Thus, in low-cost systems, since TDR cannot analyze reflections from a terminated or an active remote end, TDR cannot determine cable length even if the cable is good, i.e., even if the cable has no fault. On the other hand, although length of a cable properly terminated or connected to an active remote end can be determined using DSP, DSP fails to determine the length if the cable is too long for local and remote ends to communicate.